Certain embodiments of the present invention generally relate to electrical connectors, and more particularly to high-speed high-density board-to-board connectors.
Modular connectors exist for connecting various types of circuit boards, such as daughter cards, mother boards, back planes and the like. The modular connectors convey a densely packed number of signal lines between the circuit boards. The modular connectors each include multiple wafers or signal modules stacked in parallel. The wafers have two sides that have ground planes and signal lines formed thereon. The signal lines carry data between mating ends of the wafers, and the ground planes control impedance. The signal lines may be arranged on adjacent wafers to form differential pairs. In differential pair applications, a signal is divided and transmitted in a first direction over a pair of conductors (and hence through a pair of pins or contacts). A return signal is similarly divided and transmitted in an opposite direction over the same pair of conductors (and hence through the same pair of pins or contacts). For example, two signal lines on adjacent wafers may form a differential pair and carry a divided signal along the two signal lines.
There is a trend in board-to-board connectors toward increased data rates and line densities. Line density is a measure of differential pairs per linear inch measured along the direction perpendicular to the wafers. Generally, increasing the data rates and line density increases insertion loss and cross talk between signal lines. Ground planes reduce interference between signal lines and therefore decrease insertion loss and cross talk.
However, existing modular connectors have experienced difficulty in conveying extremely high speed data signals without severely attenuating the output signal. In particular, as data rates rise into the giga-hertz range, the signals output by the modular connectors are increasingly attenuated, such as by over 1 dB. This attenuation is also referred to as insertion loss. Attenuation is due in part to the fact that the ground planes within the connector housing develop local potentials with respect to one another during use. The buildup of the potentials between the ground planes causes the ground planes to resonate at certain frequencies, resulting in degraded throughput signals (insertion loss) and increased cross talk between signal lines on the wafers.
A need remains for an improved connector that can more adequately handle high-speed high-density data rates.
An embodiment of the present invention provides an electrical connector having a connector housing with signal modules and grounding members therein. Each signal module has a ground plane on at least one side thereof. The ground planes have contact pads formed at opposite ends thereof proximate mating ends of the signal modules. The grounding members interconnect the ground planes on adjacent signal modules to one another at a point along the ground planes or the contact pads. Optionally, the signal modules may be printed circuit boards. Alternatively, the signal modules may be pieces of molded plastic with metal traces mounted thereon.
Optionally, the signal modules may include vias having conductive liners therethrough that electrically connect ground planes on opposite sides of a signal module. The signal modules may be arranged parallel to one another within the housing. Each signal module may have one or more ground planes and one or more signal lines. Optionally, adjacent signal modules may have signal lines facing one another and forming differential pairs.
The grounding member may include pins adjoining two or more vias on two or more signal modules to one another. Alternatively, the grounding member may be a conductive rod that extends through a plurality of vias in a plurality of signal modules. The grounding member may be a metal object interposed between adjacent signal modules and may have one of spring members, dimples and beams that contact ground planes on the adjacent modules. Alternatively, the grounding member may be a metal rack having slots cut therein for receiving signal modules, where the signal modules include projections contacting ground planes on the signal modules.
An advantage of certain embodiments of the present invention is that the connector can carry large amounts of data quickly and in a very high line density with reduced insertion loss and cross talk. Because the ground planes are electrically interconnected within the connector housing by the conductive liners of the vias and the grounding members, the development of local potentials on the ground planes is minimized, thereby reducing insertion loss rates and cross talk between signal lines.